Situations frequently arise when electronic components, such as capacitors, integrated circuits, diodes, inductors, or the like, disposed on opposite sides of a substrate, such as a circuit board, microchip, or the like, are electrically interconnected by a conductor, such as a via, disposed within the substrate. The via usually passes through one or more electrically conductive planes disposed within the substrate and makes direct contact with the electrically conductive planes so that the via and electrically conductive planes are electrically connected.
One example involves a method for reducing a noise voltage on an output impedance of a power source used to power an integrated circuit (IC). The noise voltage is usually the result of a high-frequency current caused by behavior of the IC that gets passed from the IC to the power source. The noise voltage normally gets superimposed on voltages supplied by the power source to the IC. This adversely affects the performance of the IC.
The method reduces this noise by reducing the output impedance by directing the high-frequency current to ground through a capacitor connected in close proximity to the IC rather than allowing the high-frequency current to pass to the power source. In one implementation of this method, the capacitor and IC are located on opposite sides of a circuit board, and power and ground connections of the IC are connected to the capacitor using vias that pass through the circuit board. The vias connected to the ground and power connections are normally respectively connected to conductive ground and power planes disposed within the circuit board between the IC and capacitor.
It is known to those skilled in the art that high-frequency current flows substantially on the surface of a conductor and does not penetrate substantially into the interior of the conductor. Therefore, when high-frequency current flows from an electronic component on one side of a substrate, such as the IC in the above example, to an electronic component on an opposite side of the substrate, such as the capacitor in the above example, the high-frequency current flows substantially on the surface of the via. However, when the high-frequency current encounters the location where the via is connected to a conductive plane, such as the power plane in the above example, the high-frequency current changes its course so that the high-frequency current flows substantially on a surface of the plane. This is because the direct contact between the via and the plane at this location forms a solid boundary between the via and the plane that the high-frequency current cannot flow through. Therefore, the high-frequency current is forced to change its course a number of times to flow around the conductive plane and back to the via. This occurs each time the high-frequency current encounters a location where the via is connected to a conductive plane and thus causes the high-frequency current to follow an elongated, meandering path as it flows between the electronic components. One problem with this is the elongated, meandering path presents an inductance between the electronic components, and a noise voltage gets produced on impedance of the inductance as the high-frequency current flows between the electronic components.
For the reasons stated above, and for other reasons stated below that will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for reducing the impedance between electronic components disposed on opposite sides of a substrate that are electrically interconnected by a conductor passing through one or more electrically conductive planes disposed within the substrate.